<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <title>css盒子模型练习</title>
    <link href="16css.css" rel="stylesheet" type="text/css">
</head>
<body>
    <div class="top">
        <div class="topcenter">顶层中部</div>
    </div>
    <div class="middle">
        <div class="middle1">middle1</div>
        <div class="middle2">middle2</div>
    </div>
    <div class="bottom">

    </div>
</body>
</html>